That means you are using Release3 binaries with Release 8170 features usage. I don't think it make much difference changing it to Release3 with the exception of Optimizer. How Optimizer behaves depends on what were the improvements on Optimizer from 8170 to 8173 and your queries.

There will not be significant changes, you can test it if you have test instance if not go ahead and change it and be ready for 8174 upgrade if at all any consequences by changing this parmaeter. Oracle will be suggesting you to go to 8174 anyway. ;)